Smart materials such as piezoelectrics, thermoelectrics, pyroelectrics, magnetostrictives and electrostrictives are finding increased utility in adaptive structures in both commercial and non-commercial applications. In fact, smart materials are presently being utilized as actuators in such diverse products as printers, speakers, sonar equipment, adaptive optics controls, aerodynamic controls, precision pointing instruments, and for noise suppression and vibrational damping applications. Smart materials are also utilized as sensors within accelerometers, microphones, sonar systems, and vibration controls and as disposable lighter spark generators among others. This increase in the utilization of smart materials in adaptive structures is primarily due to the fact that these materials provide for direct coupling between electrical and mechanical energy.
For example, the application of an electric field to a piezoelectric or similar smart material induces a mechanical strain in the material. This is generally known as the converse piezoelectric effect relied on by electromechanical actuators. By controlling the application of the electric field to the smart material, the displacement/curvature resulting from the induced strain can be predicted and used for selective positioning, or to apply a force. However, in order to take full advantage of the converse piezoelectric effect, new methods of applying and controlling the electric field are required.
Presently, distributed electrodes are the technology of choice utilized by system designers for applying an electric field to smart materials. A typical electromechanical actuator includes a smart material layer bonded on one side to a conductive substrate in a bimorph configuration. A distributed electrode is selectively positioned and bonded to the opposite side of the smart material layer. The conductive substrate is grounded and a voltage is applied through a wire lead to the distributed electrode, thus generating an electric field across the smart material layer. The voltage, in turn, induces strain in the smart material resulting in the desired displacement/curvature. Similarly, several electrodes of varying size and shape may be selectively placed in contact with the smart material for more precise or specific control of the displacement/curvature.
Despite achieving the desired result of controlled displacement and/or curvature, utilizing distributed electrodes and wire leads to apply an electric field to the smart material layer imposes several limitations on the system designer. First, the distribution of the electrodes, their size and shape must all be predetermined early in the design process dependent upon the desired spatial resolution.
This early predetermination is problematic because once selected these features are not readily adaptable to varying system demands or requirements. For example, if a shape adjustment/correction becomes necessary on a specific region of an adaptive structure, the electrode borders must completely envelope the limits of the region or the desired adjustment/correction is impossible to achieve and redesign may be required.
Another limitation inherent in the use of distributed electrodes is restricted or low spatial resolution. With regard to the bimorph actuator described above, for example, the size of the electrode(s) strictly defines the spatial resolution of the displacement/curvature control. In order to control the curvature of a one square meter bimorph actuator with a spatial resolution of one square centimeter, ten thousand separate electrodes and their attendant wire leads would be required. Obviously, this spatial resolution is both economically and fundamentally impractical to implement and thus, severely limits the utility of these actuator devices.
Therefore, an important aspect of the present invention is to provide an apparatus/method capable of adaptively controlling the displacement and/or curvature of an adaptive structure without concern for the distribution, size and shape of electrode(s). As a result, it is now possible to overcome the cited limitations of the prior art. In doing so it is also possible to attain much higher spatial resolutions down to the order of microns.